Nanocellulose has potential as a reinforcing agent to improve stiffness and strength in polymer fiber; however, the inherent difference in hydrophilicity makes it challenging to incorporate it into nonhydrophilic polymers, and the composite properties are strongly anisotropic. In the present work, a dual approach was employed to incorporate cellulose nanofibrils (CNFs) into polylactic acid (PLA). Polyethylene glycol (PEG) acted as a compatibilizating agent to enable the melt spinning of CNF/PLA composite fibers without water/solvent, and CNFs were surface modified to improve compatibility, increase nanoparticle thermal stability, and increase CNF dispersion in PLA. While no significant difference was observed in strength, the stiffness improved up to 600% (1.3 wt % CNF, maximum draw) in the composite fibers. This improvement was correlated with the crystallinity and fiber orientation (Herman's order parameter) for as-spun and hot-drawn fibers.

Cellulose nanomaterials (CNMs) are a class of materials that have recently garnered attention in fields as varied as structural materials, biomaterials, rheology modifiers, construction, paper enhancement, and others. As the principal structural reinforcement of biomass giving wood its mechanical properties, CNM is strong and stiff, but also nontoxic, biodegradable, and sustainable with a very large (Gton yr−1) source. Unfortunately, due to the relatively young nature of the field and inherent incompatibility of CNM with most man‐made materials in use today, research has tended to be more basic‐science oriented rather than commercially applicable, so there are few CNM‐enabled products on the market today. Herein, efforts are presented for preparing and forming cellulose nanomaterial nanocomposites. The focus is on recent efforts attempting to mitigate common impediments to practical commercialization but is also placed in context with traditional efforts. The work is presented in terms of the progress made, and still to be made, on solving the most pressing challenges—getting properties that are competitive with currently used materials, removing organic solvent, solving the inherent incompatibility between CNM and polymers of interest, and incorporation into commonly used industrial processing techniques.

Cellulose nanocrystal (CNC) based composites have been explored as protective organic coatings for metal surfaces, ceramics, and wood. However, the inherent hygroscopic nature of CNCs hinders the technology from being utilized on an industrial scale as water uptake can result in soft, weak coatings. Herein, a moisture-resistant nanocomposite coating was prepared from CNCs in water and a waterborne blocked polyisocyanate (PIC). The cure temperature, which controls isocyanate deblocking and therefore cross-linking of the composite, was investigated across a wide temperature range (25–150 °C), and the subsequent films were characterized in terms of water contact angle, hygroscopic strain, and coating mechanical properties. Water contact angle measurements revealed a remarkable 3-fold reduction in hydrophilicity by cross-linking CNC with PIC. The hygroscopic strain was reduced by 20 orders of magnitude compared to untreated CNCs at 90% relative humidity (RH), which is also evidenced by static moisture sorption studies showing only a 7% moisture uptake. The mechanical and optical properties of the CNC/PIC nanocomposites were investigated to determine the physical performance of the coated material. Finally, the nanocomposite coatings exhibited a reversible humidity-dependent color change. The humidity response of these materials is potentially useful in humidity sensor applications.

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Mechanically fibrillated cellulose nanofibril (CNF) sheets of varying thicknesses were fabricated by using a wet stacking lamination technique without the use of solvents other than water or binders. The use of this technique allowed for the creation of multilayer structures with a working area of 117 mm by 117 mm and thickness of up to 0.547 ± 0.03 mm in under 2 h, which represents the shortest total processing time reported for such thickness of CNF sheets. To highlight the capabilities of utilizing wet stacking, the thickest reported 100% pure multilayer CNF sheet with a thickness of 1.65 ± 0.02 mm was produced. To gauge the effect of processing parameters on the mechanical performance of the produced sheets, thickness (85−547 μm thick), pressing time (35 min, 1 h, and 2 h), pressing pressure (0−5.17 MPa), and loading rate (4 min, 2 min, and 20 s) were varied. Tensile testing results show that the ultimate strength increased as the thickness increased and subsequently reached a plateau at a value of 207 ± 2.51 MPa at a critical thickness between 85 ± 2 and 153 ± 4 μm. A slight decrease in ultimate strength to a value of 184 ± 10.9 MPa was seen for the thicker 547 μm (0.547 mm) specimens. The specific strength was comparable to 2024 aluminum (T3 tempered) due to the relatively low density of CNF. The apparent toughness (work of failure) of the sheets was found to be on average 3.53 ± 0.36 MJ/m 3 , which is about 6 times greater than the reported value for poly(styrene). Because of their improved mechanical properties, these sheets could serve in high-strength and low-density structural applications where aluminum alloys (2024 and 6061) and packing materials/containers where commodity polymers like poly(styrene) are currently used.